4s0r
Structure of GS-TnrA complexStructure of GS-TnrA complex
Structural highlights
FunctionGLN1A_BACSU Glutamine synthetase (GS) is an unusual multitasking protein that functions as an enzyme, a transcription coregulator, and a chaperone in ammonium assimilation and in the regulation of genes involved in nitrogen metabolism (PubMed:25691471). It catalyzes the ATP-dependent biosynthesis of glutamine from glutamate and ammonia (PubMed:24158439). Feedback-inhibited GlnA interacts with and regulates the activity of the transcriptional regulator TnrA (PubMed:11719184, PubMed:12139611). During nitrogen limitation, TnrA is in its DNA-binding active state and turns on the transcription of genes required for nitrogen assimilation (PubMed:11719184, PubMed:12139611, PubMed:25691471). Under conditions of nitrogen excess, feedback-inhibited GlnA forms a stable complex with TnrA, which inhibits its DNA-binding activity (PubMed:11719184, PubMed:12139611, PubMed:25691471). In contrast, feedback-inhibited GlnA acts as a chaperone to stabilize the DNA-binding activity of GlnR, which represses the transcription of nitrogen assimilation genes (PubMed:25691471).[1] [2] [3] [4] Publication Abstract from PubMedAll cells must sense and adapt to changing nutrient availability. However, detailed molecular mechanisms coordinating such regulatory pathways remain poorly understood. In Bacillus subtilis, nitrogen homeostasis is controlled by a unique circuitry composed of the regulator TnrA, which is deactivated by feedback-inhibited glutamine synthetase (GS) during nitrogen excess and stabilized by GlnK upon nitrogen depletion, and the repressor GlnR. Here we describe a complete molecular dissection of this network. TnrA and GlnR, the global nitrogen homeostatic transcription regulators, are revealed as founders of a new structural family of dimeric DNA-binding proteins with C-terminal, flexible, effector-binding sensors that modulate their dimerization. Remarkably, the TnrA sensor domains insert into GS intersubunit catalytic pores, destabilizing the TnrA dimer and causing an unprecedented GS dodecamer-to-tetradecamer conversion, which concomitantly deactivates GS. In contrast, each subunit of the GlnK trimer "templates" active TnrA dimers. Unlike TnrA, GlnR sensors mediate an autoinhibitory dimer-destabilizing interaction alleviated by GS, which acts as a GlnR chaperone. Thus, these studies unveil heretofore unseen mechanisms by which inducible sensor domains drive metabolic reprograming in the model Gram-positive bacterium B. subtilis. Structures of regulatory machinery reveal novel molecular mechanisms controlling B. subtilis nitrogen homeostasis.,Schumacher MA, Chinnam NB, Cuthbert B, Tonthat NK, Whitfill T Genes Dev. 2015 Feb 15;29(4):451-64. doi: 10.1101/gad.254714.114. PMID:25691471[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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